01 Deja Review-Micro Protozoa

Are protozoa single cell or multicellular organisms?

Single cell. Multicellular parasites are helminths.

What structure do protozoa typically use for motility? What is the infective life form called? What is the motile form called?

Psuedopodia (false feet)
Infective form (Entamoeba and Giardia): cyst Infective form (Cryptosporidium): oocyst Motile form (Entamoeba and Giardia): trophozoite
Motile form (Cryptosporidium): sporozoite

What are the four classes of medically important protozoa?

1. Sarcodina (amebas)
2. Sporozoa (sporozoans)
3. Mastigophora (flagellates)
4. Ciliata (ciliates)

Name three protozoa that infect the intestinal tract and the diseases they cause:

1. Entamoeba histolytica causes amebiasis.
2. Giardia lamblia causes giardiasis.
3. Cryptosporidium parvum causes cryptosporidiosis.

Name a common protozoan that infects the urogenital tract and the disease it causes:

Trichomonas wginalis causes trichomoniasis.

Name some protozoa that infect blood and tissue and the diseases they cause:

Plasmodium species cause malaria, Toxoplasma gondii causes toxoplasmosis, Trypanosome species cause Chagas disease and sleeping sickness, Leishmania species cause kala-azar and cutaneous leishmaniasis, Babesia species cause babesiosis, and Naegleria fowle

How is Entamoeba transmitted?

Via fecal-oral route through cysts in water

How is the intestinal lesion of Entamoeba invasion classically described?

Flask-shaped ulcer in the colon

How does Entamoeba cause systemic disease and what is the most common organ Entamoeba invades?

Invades through the intestinal wall to enter the bloodstream. Entamoeba most commonly invades the liver forming abscesses.

What percentage of people infected with Entamoeba become symptomatic?

Approximately 10%. Ninety percent be- come carriers whose feces may contain infectious cysts.

What are the symptoms of acute amebiasis?

Dysentery (bloody, mucus-containing diarrhea), lower abdominal pain, flatulence, and tenesmus

What is treatment for amebiasis and amebic liver abscess?

Metronidazole or tinidazole. Liver abscesses do not need to be drained.

What does G. lamblia look like under the microscope?

The trophozoite form found in stool is pearshaped with two nuclei and four pairs of flagella.

How is Giardia transmitted?

Via fecal-oral route through cysts in water

Does Giardia cause systemic disease?

No. Giardia attaches to the mucosa of the duodenum, but it does not invade.

What percentage of people infected become symptomatic?

Approximately 50%. The other 50% of infected people become carriers who may continue to shed Giardia cysts in their stool for years.

Among what population is Giardia commonly found?

Children in day care centers, patients in mental hospitals, homosexuals engaging in oral-anal contact, and hikers drinking untreated stream water

What are the symptoms of giardiasis?

Nonbloody, foul-smelling diarrhea, nausea, anorexia, flatulence, and abdominal cramps, usually persisting for weeks to months

Besides microscopic examination of stool, how is giardiasis diagnosed?

By the string test (in which a weighted piece of string is swallowed and removed for microscopic examination for evidence of trophozoites), endoscopy (biopsy), and enzyme-linked immunosorbent assay (ELISA) (to detect antibodies) on stool specimens

How is it treated?

Metronidazole or tinidazole

How is C. parvum transmitted?

Via fecal-oral route through cysts in water

Does Cryptosporidium cause systemic disease?

No. Cryptosporidium attaches to the wall of the small intestine, but it does not invade.

Why is Cryptosporidium infection important in immunocompromised patients?

Cryptosporidiosis is usually self-limited in immunocompetent patients. In immunocom-promised patients, cryptosporidiosis presents as chronic, watery, nonbloody diarrhea, and leads to large fluid losses and malnutrition.

How is cryptosporidiosis diagnosed?

Fecal smear with a modified Kinyoun acid-fast stain.

What is the treatment for cryptosporidiosis?

No treatment for immunocompetent patients as the disease is self-limited. No clear effective treatment is for immunocompromised patients although there may be some benefit to start highly active antiretroviral therapy (HAART) in human immunodeficiency vir

How is T. vaginalis transmitted?

Sexual contact. There is no cyst formation in life cycle.

Where is Trichomonas found in humans?

Vagina. Prostate and male urethra

Approximately what percentage of women in the United States are carriers?

25%-50%

What are the symptoms of trichomoniasis?

Watery, foul-smelling, green vaginal discharge with itching and burning. Infected men are usually asymptomatic, though some experience urethritis.

How is trichomoniasis diagnosed? How is it treated?

Wet mount of vaginal or prostatic fluid showing motile pear-shaped trophozoites. Speculum may also demonstrate colpitis macularis (strawberry cervix). Treat both partners with metronidazole.

Name four plasmodia which cause malaria:

1. Plasmodium vivax
2. Plasmodium ovale
3. Plasmodium malariae
4. Plasmodium falciparum

Name the vector for plasmodia:

Female Anopheles mosquito

Briefly describe the life cycle of plasmodia parasite:

1.Sporozoites in mosquito saliva enter human bloodstream via mosquito bite.
2.Sporozoites enter liver cells and multiply and differentiate.
3.Merozoites are released from liver cells and enter red blood cells (RBCs).
4.Multiplication and differentiation i

Where does sexual fertilization of plasmodia occur?

Within the gut of the female Anopheles mosquito

What are the various forms of plasmodia called and where are they found?

Sporozoites (found in mosquito saliva), merozoites (found in liver cells), trophozoites (found in RBCs), hypnozoites (latent form found in liver cells), and gametocytes (found in blood)

What is the classic appearance of plasmodia within RBCs?

Rings (trophozoites are ring-shaped)

Which plasmodia cause the most severe disease?

P. falciparum

What are the classic symptoms of malaria?

Recurrent fevers, chills, and sweats

Why is malaria also referred to as blackwater fever?

Patients may experience hemoglobinuria due to extensive hemolysis and kidney damage. The dark color of the urine gave rise to the name blackwater fever.

What are other complications of malaria?

Splenomegaly from sequestration of infected RBCs, anemia, life-threatening hemorrhage from RBC hemolysis and capillary occlusion, and cerebral malaria (hemorrhage and necrosis in the brain)

What does quartan malaria refer to?

Infection by P. malariae, which typically causes fevers every third day (72-hour cycle of RBC rupture). Note that many cases do not have consistent timing of fever as there is asynchronous RBC rupture.

What does malignant tertian malaria refer to?

Infection by P. falciparum, which typically causes fever every second day (48-hour cycle of RBC rupture). However, chills and fevers may be more erratic or even continuous.

What does benign tertian malaria refer to?

Infection by P. vivax or P. ovale, which typically causes fever every second day (48-hour cycle of RBC rupture)

Which plasmodia have a latent form?

P. vivax and P. ovale

What is the difference between relapse and recrudescence?

Relapse occurs in P. vivax and P. ovale infections and results from reactivation of hypnozoites in the liver. Of patients infected with P. vivax, up to 50% relapse in a few weeks to years after initial illness. Recrudes- cence occurs in P. malariae and P.

How is malaria diagnosed?

Presence of parasites in blood smear by thick and thin blood smears (gold standard in diagnosis). Thick smears examine a drop of blood and are useful for detecting the presence of parasites; thin smears examine blood smeared across the microscope slide an

What is the drug of choice for treating nonresistant malaria?

Chloroquine

What drugs are available for chloroquine-resistant malaria?

Mefloquine, Malarone (atovaquone and pro-guanil), and quinine plus doxycycline

Why is primaquine used to treat P. vivax and P. ovale infections?

Chloroquine cannot kill hypnozoites, the latent form of P. vivax and P. ovale, but prima-quine can.

What are the methods of preventing malaria?

Preventing mosquito bites (using netting or repellant), chemoprophylaxis for travelers to endemic areas

What is the definitive host of Toxoplasma gondii?

Domestic cats (~1% of all domestic cats in the United States are carriers) and other felines

How do humans become infected with T. gondii?

Ingestion of cysts in undercooked meat from animals that grazed in soil with cat feces or from contact with cat feces. Also transplacental infection of the fetus

Do asymptomatic T. gondii-infected individuals clear the infection?

No. The parasite tends to persist as cysts within tissues.

When do the T. gondii cysts typically cause symptoms?

Immunosuppression allows activation of
bradyzoites within the cysts.

Will a mother infected with T. gondii prior to pregnancy transmit the infection to her fetus?

No. Only primary infections during pregnancy can lead to congenital infections. Infections prior to pregnancy persist in the cyst form and are not transmitted.

What are the symptoms of congenital toxoplasmosis?

Stillbirth, encephalitis, chorioretinitis leading to blindness, hepatosplenomegaly, fever, jaundice, and intracranial calcifications

How does toxoplasmosis present in immunosuppressed patients?

Typically as disseminated disease, including encephalitis

How is toxoplasmosis diagnosed?

Detection of immunoglobulin M (IgM) antibodies and multiple thin-walled ring-enhancing lesions (basal ganglion often affected) on computed tomography/magnetic resonance imaging (CT/MRI) (brain abscesses common in HIV patients)

What is the treatment of toxoplasmosis?

Sulfadiazine plus pyrimethamine

What are the three major pathogenic trypanosomes?

1. Trypanosoma cruzi
2. Trypanosoma gambiense
3. Trypanosoma rhodesiense

What disease does T. cruzi cause?

Chagas disease

What is the vector for T. cruzi?

The reduviid bug (kissing bug) as it bites around the mouth and eyes

What is Roma�s sign?

Unilateral painless periorbital swelling
("Chagoma")

Where is T. cruzi found?

Central and South America, and some parts of southern United States

What tissue is most commonly infected?

Cardiac muscle

Name some other complications of Chagas disease:

Megacolon and megaesophagus from gut neuronal damage and loss of intestinal wall tone

What is the treatment of Chagas disease?

Nifurtimox or benznidazole

What disease does T. gambiense and T. rhodesiense cause and what is the vector?

Sleeping sickness. Vector is the tsetse fly.

What are the differences between T. gambien- se and T. rhodesiense?

Trypanosoma gambiense have human reservoir and cause chronic disease. Trypanosoma rhodesiense have animal reservoir(commonly cattle and antelope) and cause an acute rapidly progressive disease.

How do trypanosomes continually evade host immunity?

Antigenic variation (variable surface gly-
coprotein)

What are the signs and symptoms of sleeping sickness? What is the treatment of sleeping sickness?

Indurated skin ulcer, cyclical fever spikes, lymphadenopathy, and progressive demyelinating encephalitis (mood changes, slurred speech, somnolence, coma). Treat with suramin.

Why must treatment be initiated before the development of encephalitis?

Suramin does not cross the blood-brain barrier. However, melarsoprol is used for encephalitis.

What are the five major pathogenic leishmanias? What is the vector?

1. Leishmania donovani
2. Leishmania tropica
3. Leishmania mexicana
4. Leishmania braziliensis
5. Leishmania major
Vector is the sand fly.

Which Leishmania causes visceral leishmaniasis (kala-azar)? What are the signs and symptoms of visceral leishmaniasis?

L. donovani. Massive splenomegaly, fever, weakness, weight loss, hyperpigmentation of skin

Which Leishmania causes cutaneous leishmaniasis? What are the signs and symptoms of cutaneous leishmaniasis?

L. tropica, L. mexicana, L. Braziliensis, and L. major. Necrotic ulcers of skin, cartilage, and mucous membranes from bite sites

What is the treatment of Leishmania infection?

Sodium stibogluconate

How does Babesia infection present?

Malaria-like symptoms because Babesia causes hemolytic anemia. Infections are most problematic in postsplenectomy patients.

What co-infection can occur with babesiosis?

Lyme disease because both are transmitted by the Ixodes tick in northeastern United States.

What is the characteristic appearance of the Babesia trophozoite within RBCs?

Maltese cross

How does Naegleria fowleri infection present?

Meningoencephalitis rapidly fatal (< 1 week), history of swimming in freshwater, amebas in cerebrospinal fluid (CSF)